A fuel cell is a power generating system directly converting chemical reaction energy of hydrogen and oxygen included in hydrocarbon-based materials such as methanol, ethanol, and natural gas to electric energy by an electrochemical reaction.
Typical examples of such a fuel cell may include a polymer electrolyte membrane fuel cell (PEMFC) or a direct methanol fuel cell (DMFC) using methanol as fuel, and the like, and developments and researches thereon have been actively progressed.
Particularly, a polymer electrolyte membrane fuel cell (PEMFC) has been accepted as a clean and efficient energy conversion system capable of being used as a movable or fixed power supply due to advantages such that a working temperature is not high, energy density is high, corrosivity is small and handling is simple.
A fuel cell system may be formed with, for example, a continuous composite of a membrane-electrode assembly (MEA), a bipolar plate collecting generated electricity and supplying fuel, and the like.
A membrane-electrode assembly is made by forming an electrode through coating a catalyst layer on an electrolyte membrane, and generally, a method of spraying catalyst slurry prepared by placing an ionomer and a catalyst in a solvent, then stirring and dispersing the result, a method of coating catalyst slurry and the like on a support first, and then transferring a produced catalyst layer on a polymer electrolyte membrane, or the like, may be used.
In order to enhance fuel cell performance, dispersibility of a catalyst and ionomer particles for a solvent is important, and direct dispersion (ball mill, bid mill or the like) and indirect dispersion (sonication), existing methods of dispersing a catalyst, have a problem in that dispersion is difficult due to problems such as aggregation when using an acetyl carbon black-based catalyst or a catalyst having a low Pt content.
In addition, a most important point in optimizing a catalyst layer structure is optimizing a tri-phase network structure of pores, a catalyst and an ionomer by the ionomer linking the catalyst particles, and with existing dispersion methods, the ionomer may be attached to the catalyst lump or readily crowded on one side, and cracks occur making the pore structure unstable leading to performance decline.
Accordingly, development of a membrane-electrode assembly capable of enhancing fuel cell performance by securing pore structure stability through highly dispersible catalyst slurry and maximally suppressing a crack phenomenon has been continuously required.